1. Field of the Invention
The present invention relates to an improvement in an automatic control system for construction machines which automatically perform leveling of ground and paving. The construction machines are used in the civil engineering and construction field and include, for example, motor graders, pavers, and bulldozers.
2. Description of the Related Art
In the civil engineering and construction field, the ground leveling implements of a construction machine, such as a blade and a screed, are automatically controlled in performing ground leveling and paving.
In the system for automatically controlling a ground leveling implement that is used in a construction machine, a ground leveling string corresponding to a finished cross section is stretched over the construction side in order to obtain an expected finished surface. The interval between the ground leveling string and the ground leveling implement is detected with a contact type cantilever or a non-contact type ultrasonic sensor. Based on the detection result, the ground leveling implement is controlled so as to follow the ground leveling string by oil pressure. However, the system for automatically controlling a ground leveling implement so that the implement follows a ground leveling string requires a great deal of labor to stretch a ground leveling string over a construction site.
Hence, there has been proposed an automatic control system for construction machinery which is capable of automatically controlling a ground leveling implement and obtaining an expected finished surface without stretching a ground leveling string over a construction site.
An example of the aforementioned automatic control system is shown in FIG. 1. In the figure, reference numeral 1 denotes a bulldozer which is a construction machine for leveling a construction site, 2 a rotating laser unit installed in a construction site, 3 a blade which is a ground leveling implement, 4 a pole stood up in the blade 3, and 5 a laser sensor fixed to the pole 4.
The rotating laser unit 2 forms a reference plane Rs at a position of a predetermined height (h) away from a finished plane 6 by means of a generated laser beam. The blade 3 is controlled so that the laser light from the rotating laser unit 2 strikes against the vertical center Ho of the laser sensor 5 (center Ho in the height direction of the laser sensor 5), by an oil pressure control unit 7 serving as ground leveling implement control means. In this way, the ground of a construction side is leveled to an expected finished plane 6. According to this automatic control system for construction machines, a ground leveling operation and a paving operation can be simply performed compared with an operation of stretching a ground leveling string over a construction site.
However, in the case where the ground 6' and finished plane 6 of a construction site have a complicated configuration with undulations and inclination, the rotating laser unit 2 has to be reinstalled as shown in FIG. 2 in order to obtain the reference plane Rs. For this reason, in the case of the leveling and paving of complicated ground, there will arise the problem that the operation for reinstalling the rotating laser unit 2 will be troublesome.
Hence, another system for automatically controlling the construction machine 1 has been proposed. This system employs an automatic tracking type survey unit, also called a total tracking station (which is available as "AP-L1" manufactured by TOPCON). The automatic tracking type survey unit measures a distance to a target, a horizontal angle between a reference direction and a direction in which the target exists, and a vertical angle between a reference height and a direction in which the target exists, and tracks the target.
FIG. 3 illustrates an example of the system for automatically controlling a construction machine by employing an automatic tracking type survey unit. In the figure, reference numeral 8 denotes an automatic tracing type survey unit, which is installed at the known coordinate point O of a construction block. The survey unit 8 is connected to a personal computer (PC) 9, which is in turn connected to a radio transmitter 10. A bulldozer 1 is provided with a blade 3, a pole 4 stood up in the blade 3, an oil pressure control unit 7, a prism 11 attached to the pole 4 as a target to be tracked, and a radio receiver 12.
The PC 9 stores finished-height data in correspondence with each horizontal coordinate position in the construction block. The survey unit 8 tracks the prism 11 and measures the distance from the known coordinate position O to the prism 11 and the horizontal angle between a reference direction and a direction in which the prism 11 exists. Based on the measured distance and horizontal angle, the survey unit 8 computes the coordinate position data or horizontal coordinate position data of the prism 11 (target) relative to the known coordinate O. The computed coordinate position data or horizontal coordinate position data is transferred from the survey unit 8 to the PC 9.
The PC 9 calls out finished-height data corresponding to the computed horizontal coordinate position, that is, finished-height data relative to the known coordinate point O. Then, the PC 9 transfers the finished-height data to the radio transmitter 10. The radio transmitter 10 transmits the finished-height data to the radio receiver 12. The oil pressure control unit 7 controls the blade 3, based on the finished-height data received by the radio receiver 12. The blade 3 digs or cuts ground so that the ground has a designed finished height (construction height). Note that the aforementioned finished-height data is referred to as a height relative to known coordinate point O.
The system for automatically controlling a construction machine with the automatic tracing type survey unit 8 has the advantage that the finished plane of complicated ground can be created without increasing the number of steps, because the blade 3 is controlled based on finished-height data (construction data).
However, in a construction site the operators are in contact with each other by using transceivers and there is radio noise developed by construction machines. The aforementioned system always requires a unit which transmits construction data from the survey unit 8 to the bulldozer 11 in a construction site by radio. Therefore, there is the possibility that interference and communication jamming will take place, and reliability will be a problem.